1. Field of the Invention
The present invention relates to a supply/conveyance mechanism for sheets, such as printable material or printed material, by which a plurality of sheets stacked in layers are successively supplied or conveyed, in alignment, one by one.
2. Description of the Related Art
An automatic document feeder is used in mechanisms, such as a facsimile machine, a copier or an image scanner, having an image input section through which document images are input. According to the automatic document feeder, a large number of documents stacked in a hopper can be automatically processed. Therefore, automatic document feeders are widely used in offices and used for various purposes.
Such an automatic sheet feeder includes a hopper in which documents or sheets are stacked; a picking section in which documents are picked up, one by one, by a picking roller or the like; a separating section for preventing double feeding of documents sent from the picking section; a processing section in which the documents sent from the picking section are subjected to the process of reading or printing; a stacking section in which the processed documents are stacked; and a conveyance section for conveying the documents from the separating section to the stacking section through the processing section. Further, it is required to provide a driving section composed of a motor for driving these sections, a sensor section for detecting the positions of documents, and a control section for controlling these sections. By the actions of these sections described above, images on the document can be precisely read and input.
In the conventional supply/conveyance mechanism for sheets, the stacking of documents is improved in the following manner.
In the case of a low speed machine in which sheets of paper of regular sizes, such as A4 size and A5 size, are handled, a sheet stacking surface in the stacking section is inclined by an angle of 15.degree. to prevent the documents from dropping. Alternatively, a gap between the sheet guides of the discharge section is formed into a V-shape so that the discharged documents are intentionally curved for enhancing the rigidity thereof, and thereby the rotation and inversion of documents can be avoided. Alternatively, a small document stopper is provided for preventing the documents from being scattered in the process of stacking.
However, since the conveyance speed of recent apparatus is high and the number of documents to be processed is also high, and since it is required to process documents of various sizes, from small documents of A8 size to relatively large documents of A3 size, the conventional measures described above are not sufficient to meet the demands.
Concerning the skew of conveyed documents, in the case of a low speed machine, after the document has begun to feed, the rotation of the conveyance roller is stopped, so that a front end, or leading edge, of the stopped document comes into contact with the conveyance roller. In this way, the leading edge of the document is aligned with the conveyance roller. Therefore, any skew of the document can be reduced. However, in the case of a high speed machine, a large amount of time is required for the aligning operation, and the documents flutter because the document conveyance speed is high. Therefore, the aligning effect is relatively low. For this reason, it is difficult to adopt the aforementioned aligning operation.